The invention refers to optical components such as ophthalmic lenses or semi-finished lens blanks for ophthalmic lenses.
It is well known that such optical components comprise two surfaces having each, geometrical features adapted to form in combination an optical system suitable to attenuate/correct visual defects of a wearer.
The optical component has at least one of following surfaces: spherical surface, aspherical surface, sphero-toric surface, progressive surface, surface comprising a plurality of segments.
For example, among the geometrical features there are the curvature radii of at least one of these surfaces which can vary from one to other points of these surfaces. Indeed, a multisegment lens has a surface having a plurality of area, each area having a constant curvature radius usually called a segment. Thus, the number of segments of a lens is a geometrical feature which allows identifying if an ophthalmic lens or a semi-finished lens blank for ophthalmic lens is either a single vision or bifocal or trifocal lens. A progressive lens has a continuous varying curvature radius. A single vision lens has a spherical or aspherical or sphero-toric surface.
These geometrical features make it possible to characterize surfaces of the optical component and thus to identify them.
It is well-known methods of measurement of the geometrical structure of an optical component.
For example, method and system of mechanical palpation make it possible to determine the three-dimensional structure of a lens with a very high degree of accuracy. This method consists in placing a mechanical probe in direct contact with the surface of the lens then to memorize the position of contact probe-surface. This operation is repeated several hundreds of times on lens.
Nevertheless, this method is very long. For example, it requires approximately 20 minutes per face of the optical component. Moreover, it requires sometimes a destroying sample preparation, for example by fixation of lenses with glue.
Furthermore, its use requires calling upon expert operators and in a very constrained environment. Thus, it is not very compatible with a fast measure carried out in a laboratory of manufacture.
Optical methods also exist to determine with precision the surface of a lens knowing other surface. For example, the patent application WO 02/16902 A1 describes a method and an apparatus for transmission measurement of the geometric structure of an optical component. The described method makes it possible to measure one or more polished surfaces or the distribution of index of an optical component. Nevertheless, this method is expensive to implement.
Consequently, there is a need for a method making it possible to identify fastly and in a reliable manner geometrical features of optical components such as lenses or semi-finished lens blanks.